A switched-mode power supply voltage regulator uses energy storage elements (e.g., capacitors, inductors) and switching elements (e.g., transistors) to generate a regulated output voltage from an input voltage. In particular, a boost regulator generates an output voltage that is generally higher than the boost regulator input voltage, while buck-boost (also referred to as inverted boost) regulators may have an output voltage that is higher or lower than the buck-boost regulator input voltage and may also be of opposite polarity.
A switched-mode power supply repeatedly switches between two states: an on-state and an off-state. During the on-state, the regulator input voltage has a direct electrical path to charge an energy storage element and/or to power a load. During the off-state, the input is electrically disconnected from the charged energy storage element, which discharges the stored energy to provide power to the load. Typically, one or more transistors act as the switching elements to control the timing and duration of the on-states and the off-states. The states of the transistors may be controlled by driver circuits, which turn the transistors on and off according to an input signal. The output voltage may be controlled by the frequency and relative duration of the on and off-states.
Within an integrated circuit (IC), die area can be a scarce commodity. A frequent goal of IC fabrication is to make the components on the die as small as possible. A limitation of smaller components is that the amount of semiconductor material used in a semiconductor device decreases. Thus, less energy is required to destroy the device.
Currently, for a switched-mode power supply to work in boost and buck-boost modes of operation, the designer uses two pre-driver circuits per output transistor. In an example case having two output transistors in a regulator, four pre-driver circuits are required. Additionally, the pre-drivers must be independent of each other so that when one pre-driver is active (e.g., the boost mode pre-driver), the other pre-driver (e.g., the buck-boost mode pre-driver) is disconnected to avoid damage. Multiple pre-drivers require very complex pre-driver control circuitry at the expense of die space, which may substantially increase the size of the circuit.